The present invention relates to a reference wavelength light generating apparatus for generating predetermined reference wavelength light in an optical spectrum analyzer and so on.
Normally, a measuring apparatus such as an optical spectrum analyzer performing various measurements by using a predetermined measuring beam often displays measurement results in a graphical form with its horizontal axis corresponding to wavelengths and its vertical axis corresponding to detection levels. In case of displaying such measurement results, there are cases where wavelengths of the horizontal axis deviate over time due to environment such as temperature. For this reason, wavelengths are adjusted to the horizontal axis by using predetermined reference wavelength light of which wavelength has a known absorption spectrum. An apparatus for generating reference wavelength light to be used for such calibration is the reference wavelength light generating apparatus.
FIG. 9 is a diagram showing configuration of a conventional reference wavelength light generating apparatus used for an optical spectrum analyzer and so on. Reference wavelength light generating apparatus 200 shown in FIG. 9 is intended to simultaneously generate predetermined reference wavelength light used for calibration and a predetermined measuring beam used for measurement, and is comprised of two light sources 210, 240, two fiber collimators 212, 214 and an optical cell 216.
The two light sources 210, 240 are formed by using an edge emitting type LED for instance. The light source 210 on the one hand is used to generate reference wavelength light, and the light emitted from this light source 210 is let into the fiber collimator 212 via an optical fiber 220 and is converted into parallel rays. These parallel rays pass through the optical cell 216 to have predetermined wavelength components absorbed. The parallel rays after passing through the optical cell 216 are led to an optical connector for reference wavelength light 230 via an optical fiber 222 after having their light gathered by the other fiber collimator 214. Moreover, the other light source 240 is used to generate a measuring beam, and any light emitted from this light source 240 is led to an optical connector for measuring beam 252 via an optical fiber 224.
Incidentally, there has been a problem that, in the above-mentioned conventional reference wavelength light generating apparatus, adjustments are not easy as to the two fiber collimators 212 and 214 placed sandwiching optical cell 216. To have the parallel rays emitted from fiber collimator 212 on the one hand exactly let into the other fiber collimator 214, the horizontal and vertical positions of the two fiber collimators as well as their respective angles of inclination must be adjusted. As there are so many points to be adjusted and adjustments of the adjusted angles and horizontal and vertical positions must be made simultaneously, it is not easy to perform desired adjustments exactly.
In addition, in the above-mentioned conventional reference wavelength light generating apparatus, there has been a problem that two light sources 210, 240 and two fiber collimators 212, 214 which are relatively expensive parts are used in order to generate reference wavelength light and a measuring beam so that production cost increases. For instance, a SELFOC lens that is a relatively expensive part is used for the above-mentioned fiber collimators 212, 214 affixed to one end each of the above-mentioned optical fibers 220, 222.
The present invention was devised in consideration of such points, and its object is to provide a reference wavelength light generating apparatus allowing time and effort for adjustments to be reduced and also capable of cost cutting by reducing the number of parts.
In order to attain the above-mentioned object, the reference wavelength light generating apparatus of the present invention is equipped with a light source for generating light having a predetermined wavelength range, an absorbing member for absorbing a predetermined wavelength component from incident light, a reflecting member for reflecting any light emitted from the above described absorbing member in the direction of the above described absorbing member, light branching unit for branching and emitting the light emitted from the above described light source in both a direction of the above described absorbing member and a direction different from that of the above described absorbing member and also branching and emitting the light incident from the above described absorbing member in both a direction of the above described light source arid a direction different from that of the above described light source, and a collimator for converting the light emitted from the above described light branching unit to the above described absorbing member side via an optical fiber into parallel rays at the end of the above described optical fiber and letting them into the above described absorbing member, in which the light branched from the above described light branching unit in a direction different from that of the above described light source is emitted as reference wavelength light and the light branched from the above described light branching unit in a direction different from the above described absorbing member is emitted as a measuring beam. As the light reflected by the reflecting member can be accurately let into the absorbing member again merely by adjusting an angle of the reflecting member, it can significantly reduce time and effort for adjustments required for generating reference wavelength light. In addition, as it can generate reference wavelength light and a measuring beam by using one light source, cost cutting by reducing the number of parts is possible. Moreover, the light having been converted into parallel rays by the collimator can easily proceed along a reverse optical path by passing through the absorbing member and then being reflected by the reflecting member. In particular, as the number of collimators used for letting into and emitting light to and from the absorbing member can be only one, the number of collimators, which is a relatively expensive component, can be reduced compared with a conventional case where two collimators in total are used at both ends of the absorbing member, so that cost cutting thereby is possible.
The reference wavelength light generating apparatus of the present invention is equipped with a light source for generating light having a predetermined wavelength range, an absorbing member for absorbing a predetermined wavelength component from incident light, a reflecting member for reflecting any light emitted from the above described absorbing member in the direction of the above described absorbing member, light branching unit for emitting the light emitted from the above described light source in a direction of the above described absorbing member and also branching and emitting the light incident from the above described absorbing member in both a direction of the above described light source and a direction different from that of the above described light source, and a collimator for converting the light emitted from the above described light branching unit to the above described absorbing member side via an optical fiber into parallel rays at the end of the above described optical fiber and letting them into the above described absorbing member, in which the light branched from the above described light branching unit in a direction different from that of the above described light source is emitted as reference wavelength light. As the light reflected by the reflecting member can be accurately let into absorbing member again merely by adjusting an angle of the reflecting member, it can significantly reduce time and effort for adjustments required for generating reference wavelength light. In addition, the light having been converted into parallel rays by the collimator can easily proceed along a reverse optical path by passing through the absorbing member and then being reflected by the reflecting member. In particular, as the number of collimators used for letting into and emitting light to and from the absorbing member can be only one, the number of collimators, which is a relatively expensive component, can be reduced compared with a conventional case where two collimators in total are used at both ends of the absorbing member, so that cost cutting thereby is possible.
Especially, in the case where the above-mentioned light source is comprised of an edge emitting type LED and the collimator is comprised of a SELFOC lens, the cost cutting effect by reducing the number of these expensive components is great.
Furthermore, the above-mentioned light branching unit has a light power branching ratio set so that power of the light emitted to the above described absorbing member side becomes lower than power of the light emitted to a direction different from that of the above described absorbing member. It is possible, by setting the light power branching ratio in this manner, to set the power of the measuring beam high. In addition, as it allows return light to the light source side from the absorbing member side to be reduced, it can prevent the light source from becoming unstable.